Deep vein thrombosis is a common condition that often presents a diagnostic challenge to clinicians. Seventy five per cent of outpatients who present with signs and symptoms suggestive of deep vein thrombosis do not have the disease.1,2
Most clinics and emergency facilities rely on venous ultrasound imaging as the initial diagnostic test of choice.3
One way to improve care and at the same time reduce the burden of ultrasound testing is to use a combination of two simple tests that, when combined, accurately exclude deep vein thrombosis. This use of two independent tests, each of which has high negative predictive value for a disease, is extremely useful in ruling out disease.4
Researchers into venous thrombosis now use this approach, combining d
-dimer testing with estimation of the clinical probability of deep vein thrombosis.
-dimer is one of the fibrin degradation products generated during fibrinolysis. d
-dimer concentrations are raised in the setting of acute deep vein thrombosis,5
and normal concentrations are expected in the absence of acute venous thrombosis unless other, coexistent conditions that activate the coagulation system are present.6-9
Newer, less sensitive, whole blood, qualitative agglutination assays, particularly the SimpliRED d
-dimer test (Agen Biomedical, Brisbane, Australia), and more highly sensitive, quantitative, enzyme linked inmmunosorbent assays (ELISAs) are sufficiently rapid for use in outpatients.10,11
Two clinical probability tools to estimate the probability of venous thrombosis are widely used. The first, developed by Wells et al,2,12
uses a structured assessment of explicit historical and physical examination criteria (box) to stratify patients into low, moderate, and high risk of deep vein thrombosis.
A second clinical probability tool, developed by Perrier et al,13,14
also stratifies patients into the same three rating categories by using semistructured, implicit criteria. When each of these tools was used, fewer than 3% of patients with low probability and fewer than 19% of patients with moderate probability had a deep vein thrombosis.12,13
A modified version of the Wells tool, which collapses the three risk categories into two—deep vein thrombosis likely and deep vein thrombosis unlikely—has been developed recently.15
Wells clinical probability tool
Wells explicit assessment
- Active cancer
- Paralysis, paresis or recent plaster, or immobilisation of lower limb
- Recently bedridden for more than three days or major surgery in the past four weeks or more
- Localised tenderness
- Entire leg swollen
- Calf swelling > 3 cm compared with asymptomatic leg
- Pitting oedema
- Collateral superficial veins
- Alternative diagnosis as likely or greater than deep vein thrombosis
Each positive response is 1 point, except if an alternative diagnosis is as likely as or greater than DVT, where 2 points are deducted. 0 or fewer points: low probability; 1-2 points: moderate probability; 3 or more points: high probability.
Two general approaches have been used to evaluate the combined use of rapid d
-dimer testing and clinical probability estimates.5
Firstly, accuracy studies have been conducted in which all patients underwent complete testing, and the results of each test were compared with the accepted criterion standard.16
Secondly, management studies have been reported in which patients were initially stratified into a low risk group and higher risk groups, on the basis of the result of either the d
-dimer test or the clinical probability tool, and only the patients at higher risk were tested further by using the criterion standard. In these studies, patients classified as at low risk were simply followed over time to determine the incidence of thromboembolism.
This systematic review focuses on clinical studies that have evaluated the use of rapid d
-dimer testing in conjunction with assessment of clinical probability.17
The primary outcome measure was the incidence of objectively confirmed symptomatic deep vein thrombosis and pulmonary embolism among patients with a normal d
-dimer test result, stratified by the level of clinical probability.